A technique for transmitting rotations of a certain driving shaft to another driving shaft via a driving medium such as a belt and a chain is employed. In such a driving force transmission apparatus, a tensioner is used to set the tension of driving medium to be an appropriate level. The tensioner adjusts the tension of the driving medium to be appropriate by biasing the driving medium with a biasing member, for example, a compression spring.
As reference techniques of the tensioner, the following patent literatures 1 and 2 are cited.